She later slashed her own wrist, leaving a note in which she told Lewis's father: "Enjoy your life now, nothing is stopping you, ha ha ha."

The bodies were found at separate addresses in Tipton, West Midlands, on Sunday December 9 last year, the inquest at the Council House heard.

Black Country Coroner Robin Balmain heard that Lewis died of poisoning, with high levels of a painkiller, Tramadol, discovered in his blood and urine.

Lewis's father, Shaun Dangerfield, who had split from Ms Hart and had a new partner, said the last text he received from her in the days before the deaths read: "I know what to do now for the best" and was signed with a kiss.

The 27-year-old said that at the time he thought it was an "amicable" response to a disagreement they had had over Lewis's custody arrangements.

But the inquest heard that, in a note left by Ms Hart, she told him: "Did you really think I was going to die and allow you to bring Lewis up and play happy families? You made your choice and now you can live with it."

As relatives wept in the courtroom, the coroner said it was "simply spite" that motivated Ms Hart's actions. Mr Balmain said: "She was prepared to kill her son to spite Mr Dangerfield. I cannot imagine anything so evil as a mother who would be prepared to do that."

The coroner recorded that Ms Hart had killed herself, with haemorrhaging as the cause of death, while the poisoning of Lewis was recorded as an unlawful killing.